A fuel cell system usually comprises a fuel cell stack, which has a plurality of fuel cell elements stacked up one upon the other. Each fuel cell element comprises an electrolyte, which separates an anode space from a cathode space. In an SOFC fuel cell, the electrolyte consists of a ceramic material. It is connected to a metallic frame in order to tap the electric current. The individual fuel cell elements are rigidly connected to one another via the metal frame in order to form the fuel cell stack.
Based on different expansion properties, it may happen during the heating of the fuel cell stack that the individual fuel cell elements will bulge or be deformed. This may lead, on the one hand, to rupture of the electrolyte, which is associated with an unintended leakage of cathode gas in the direction of the anode gas or vice versa. The subsequent reaction will then no longer take place electrochemically, but according to combustion. This may lead to destruction of the fuel cell system and possibly of the vehicle equipped therewith. On the other hand, deformation of the fuel cell elements leads to impaired electric contacting between the electrolyte and a corrugated metal plate, via which the electric current is tapped. For example, a contact paste is applied to improve contacting between the particular electrode and the corrugated metal plate. The deformation of the fuel cell elements will then be accompanied by a deformation of the corrugated metal plates, as a result of which contacting will decrease greatly. As a consequence, the electric current can be transmitted at individual contact surfaces only, which may lead to local overheating and to damage to the fuel cell.